Screw rotor processing method and screw rotor lead correction calculation device

Abstract

A screw rotor lead correction calculation device includes an initial data input section configured to input an error as a distance with respect to a reference lead at each axial position of a rotor groove portion of a screw rotor, and a processing machine input correction amount/position output section configured to compute and output, based on the error as the distance input to the initial data input section, a lead correction amount with respect to the reference lead and a lead correction starting position as an axial position for starting lead correction. With this configuration, correction data for obtaining a screw rotor with a high-accuracy lead can be obtained from a lead error with respect to a reference lead in a screw rotor obtained by ground finish of the material of the screw rotor.

The invention claimed is: 
     
       1. A screw rotor processing method for correcting a lead error of a screw rotor to process the screw rotor, comprising:
 grinding a material of the screw rotor; 
 measuring, as a distance, the lead error with respect to a reference lead at an axial position of a rotor groove portion of the screw rotor produced by grinding; 
 wherein a lead correction amount for correction of the lead error and a lead correction starting position as an axial position of the screw rotor for starting the lead correction are calculated based on the lead error measured as the distance, including
 obtaining a rotation angle θ on the reference lead at the axial position of the rotor groove portion and a rotation angle dθ corresponding to a lead error at the position with the rotation angle θ, 
 obtaining a correction point, by means of a rotation angle −dθ obtained by inverting a sign of the rotation angle dθ corresponding to the lead error, as a difference from the rotation angle θ, and 
 obtaining the lead correction amount from a correction lead passing through the correction point and the lead correction starting position from the rotation angle θ; and 
 
 grinding the screw rotor based on the calculated lead correction amount and the calculated lead correction starting position. 
 
     
     
       2. The screw rotor processing method according to  claim 1 , wherein
 the material of the screw rotor is ground by a grinding machine having a grinding stone, 
 the lead correction amount and the lead correction starting position are calculated as a lead correction amount with respect to the reference lead at each axial position of the rotor groove portion of the screw rotor and a lead correction starting position for starting the lead correction, and 
 data on the calculated lead correction amount and the calculated lead correction starting position is provided to the grinding machine to grind the material of the screw rotor. 
 
     
     
       3. The screw rotor processing method according to  claim 2 , wherein
 the lead correction starting position is determined by a position at which the grinding stone of the grinding machine contacts on the screw rotor. 
 
     
     
       4. The screw rotor processing method according to  claim 1 , wherein
 when a rotation angle to be corrected at a position with a rotation angle θ i  on the reference lead is dθ i , a distance at a position in a Z-direction as an axial direction is Z i , the lead correction amount is dP, and the reference lead is P 0 , the lead correction amount dP is obtained by the following equation (Expression 1): 
 
       
         
           
             
               
                 
                   
                     
                       [ 
                       
                         Expression 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                       
                       ] 
                     
                     ⁢ 
                     
                         
                     
                   
                 
                 
                   
                       
                   
                 
               
               
                 
                   
                     
                       dP 
                       = 
                       
                         
                           
                             2 
                             ⁢ 
                             
                               π 
                               ⁡ 
                               
                                 ( 
                                 
                                   
                                     Z 
                                     
                                       i 
                                       + 
                                       1 
                                     
                                   
                                   - 
                                   
                                     Z 
                                     i 
                                   
                                 
                                 ) 
                               
                             
                           
                           
                             
                               ( 
                               
                                 
                                   θ 
                                   
                                     i 
                                     + 
                                     1 
                                   
                                 
                                 + 
                                 
                                   d 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     θ 
                                     
                                       i 
                                       + 
                                       1 
                                     
                                   
                                 
                               
                               ) 
                             
                             - 
                             
                               ( 
                               
                                 
                                   θ 
                                   i 
                                 
                                 + 
                                 
                                   d 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     θ 
                                     i 
                                   
                                 
                               
                               ) 
                             
                           
                         
                         - 
                         
                           P 
                           0 
                         
                       
                     
                     ⁢ 
                     
                       
 
                     
                     ⁢ 
                     
                       
                         i 
                         = 
                         0 
                       
                       , 
                       1 
                       , 
                       2 
                       , 
                       … 
                       ⁢ 
                       
                           
                       
                       , 
                     
                   
                 
                 
                   
                     ( 
                     
                       Expression 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                     ) 
                   
                 
               
             
           
         
         where an index i indicates an order of a measurement point at which the lead error with respect to the reference lead at the Z-direction position of the rotor groove portion has been measured, and “i=0” corresponds to an origin of the rotation angle or the Z-direction position. 
       
     
     
       5. The screw rotor processing method according to  claim 1 , wherein
 the lead correction amount and the lead correction starting position are calculated using measurement data on a lead error of one of two surfaces forming a groove of the screw rotor.